Abstract

he cheetah (Ch, Acinonyx jubatus) is a species considered globally endangered and cloning is one of the assisted reproductive techniques that can help to preserve it and to study early embryo development. However, the production of cloned felid embryos remains inefficient, probably because of the difficulty to control the process of nuclear reprogramming and obtain adequate gene expression. Embryo aggregation has been demonstrated to improve the cloning efficiency in several species and to normalise cdx2 in the mouse by lowering its expression (Balbach et al. 2010), but it has not been evaluated in felids before. To better understand the effect of interspecific somatic-cell nuclear transfer (iSCNT) and embryo aggregation in nuclear reprogramming, we analysed the expression of oct4, sox2, nanog, and cdx2 in cheetah blastocysts generated by iSCNT, domestic cat blastocysts (Dc) generated by SCNT, and IVF blastocysts as control. To achieve this, domestic cat oocytes were in vitro matured and zona-free SCNT or iSCNT was performed, as previously described (Moro et al. 2014, Reprod. Fertil. Dev.). Zona-free reconstructed embryos were then cultured individually (1X) or two embryo were cultured together (2X) in microwells, in synthetic oviductal fluid (SOF) medium. The experimental groups were Dc1X, Dc2X, Ch1X, Ch2X, and IVF. After 8 days of in vitro culture the blastocysts obtained were stored in RNA-later at –20°C. For gene expression analysis, blastocysts were pooled as follows: Dc1X, 4 replicates of 3 blastocysts each; Dc2X, 4 replicates of 3 blastocysts each; Ch1X, 2 replicates of 2 blastocysts and 1 replicate of 1 blastocyst; Ch2X, 4 replicates of 3 blastocysts each; IVF 3 replicates of 3 blastocysts each. Embryos were treated with a Cells-to-cDNA TM II kit (Life Technologies, Carlsbad, CA, USA) lyses buffer and treated with DNase I (0.04 U μL–1) for genomic DNA digestion. Gene expression analysis was performed by real-time qPCR using the standard curve method. In all qPCRs, GAPDH was used as an internal control. The statistical analysis was performed using a non-parametric Kruskal–Wallis test (P < 0.05). We observed that Dc1X blastocysts overexpressed the 4 genes evaluated respect to the IVF control. However, the gene expression of the aggregated group (Dc2X) was lower for all the genes, achieving the same levels of nanog and sox2 as the IVF blastocysts. The expression of oct4 and cdx2 were also closer to the expression levels of the control in the Dc2X group than in the Dc1X group. With respect to interspecific embryos, the amount of oct4 and cdx2 was also significantly reduced in the Ch2X blastocysts respect to Ch1X blastocysts. Both cheetah groups showed significantly lower expression of oct4, cdx2, and nanog than the IVF control. In conclusion, transcription of pluripotent and early differentiation factors in cheetah embryos was not as efficient as in the domestic cat embryos, probably caused by interspecific transfer. Our study demonstrated for the first time that defects in gene expression of domestic cat embryos can be corrected by embryo aggregation, providing a simple strategy to improve felid cloning.